U.S. patent number 10,253,750 [Application Number 15/283,814] was granted by the patent office on 2019-04-09 for controller for pendulum type wave-power generating apparatus.
This patent grant is currently assigned to KOREA INSTITUTE OF OCEAN SCIENCE & TECHNOLOGY. The grantee listed for this patent is Korea Institute of Ocean Science & Technology. Invention is credited to Key-Yong Hong, Seung-Ho Shin, Tomiji Watabe.
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United States Patent |
10,253,750 |
Shin , et al. |
April 9, 2019 |
Controller for pendulum type wave-power generating apparatus
Abstract
The present invention provides a controller for a pendulum type
wave-power generating apparatus. Electric power produced by
wave-power generation has been pointed out as being of low
efficiency and more expensive than wind-power generation. To
overcome the above problems, the present invention uses resonance
and impedance matching of the sea waves, thus making it possible to
markedly enhance the efficiency of wave-power generation. The
present invention does not use a wave-height meter which is
generally expensive and controls the generating apparatus in
response to variation of the conditions of the sea, thus
automatically maintaining the resonance and impedance matching
operation, thereby making high-efficiency operation possible. As a
result, the cost of the wave-power generation can be reduced, so
that the wave-power generation can be widely commercialized.
Inventors: |
Shin; Seung-Ho (Daejeon,
KR), Hong; Key-Yong (Daejeon, KR), Watabe;
Tomiji (Hokkaido, JP) |
Applicant: |
Name |
City |
State |
Country |
Type |
Korea Institute of Ocean Science & Technology |
Ansan |
N/A |
KR |
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Assignee: |
KOREA INSTITUTE OF OCEAN SCIENCE
& TECHNOLOGY (Ansan, KR)
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Family
ID: |
46969629 |
Appl.
No.: |
15/283,814 |
Filed: |
October 3, 2016 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20170089320 A1 |
Mar 30, 2017 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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13512697 |
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PCT/KR2011/005269 |
Jul 18, 2011 |
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Foreign Application Priority Data
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Apr 8, 2011 [KR] |
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10-2011-0032891 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F03B
13/22 (20130101); F15B 11/16 (20130101); F03B
13/182 (20130101); F15B 1/04 (20130101); F15B
13/06 (20130101); F03B 15/02 (20130101); F03B
15/00 (20130101); Y02E 10/30 (20130101); F05B
2220/706 (20130101); F15B 2211/50 (20130101); F05B
2260/406 (20130101) |
Current International
Class: |
F03B
13/18 (20060101); F15B 13/06 (20060101); F03B
15/00 (20060101); F15B 1/04 (20060101); F15B
11/16 (20060101); F03B 15/02 (20060101); F03B
13/22 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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09144642 |
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Jun 1997 |
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JP |
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19910008279 |
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May 1991 |
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KR |
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1020040027662 |
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Apr 2004 |
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KR |
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Other References
PCT International Search Report dated Mar. 28, 2012, for related
application PCT/KR2011/005269. cited by applicant.
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Primary Examiner: Lopez; F Daniel
Attorney, Agent or Firm: Fredrikson & Byron, P.A.
Parent Case Text
RELATED APPLICATIONS
This is a continuation of application Ser. No. 13/512,697, filed
May 30, 2012, which is a 35 U.S.C. 371 national stage filing from
International Application No. PCT/KR2011/005269 filed Jul. 18,
2011, and claims priority to Korean Application No. 10-2011-032891
filed Apr. 8, 2011, the teachings of each of which are incorporated
herein by reference.
Claims
The invention claimed is:
1. A pendulum type wave-power generating apparatus converting a
pendulum motion of wave-power energy into a rotary motion using a
hydraulic transmission that has pressure accumulators (31) and (41)
on a hydraulic circuit thereof, thus operating a generator (60), a
controller comprising: pressure control valves (33) and (43)
controlling output volumes of hydraulic motors (32) and (42) that
operate the generator (60) such that the output volumes are
corresponding to hydraulic pressures in pipes (30) and (40) of the
hydraulic circuit so that a mean value of wave power energy input
into the hydraulic circuit is equal to a mean value of a drive
force of the generator (60), whereby wave-power energy is able to
be used regardless of a variation in wave conditions on the sea,
wherein each of the pressure control valves (33) and (43)
comprises: a first port (100) connected to the corresponding pipe
(30), (40) of the hydraulic circuit so that hydraulic pressure
(PI), (P2) is input into the first port (100); a cylinder (110)
into which the hydraulic pressure (PI), (P2) is applied from the
first port (100); a damper (111) installed in the cylinder (110),
the damper (111) being moved upwards or downwards by the hydraulic
pressure (PI), (P2) applied thereto from the first port (100); a
third elastic member (113) contracted by the hydraulic pressure
(PI), (P2) applied to the damper (111) from the first port (100); a
chamber (120) in which a spool (122) is moved upwards or downwards
by the damper (111), thus increasing or reducing a valve pressure
(P3) in the chamber (120); first and second elastic members (121)
and (123) respectively installed on and under the spool (122), the
first and second elastic members (121) and (123) being expanded or
contracted depending on movement of the spool (122); a second port
(130) through which the hydraulic pressure (PI), (P2) of the
hydraulic circuit is applied into the chamber (120); a third port
(140) which relieves the valve pressure (P3) from the chamber (120)
to an outside; and a fourth port (150) communicating with the
second port (130) or the third port (140) depending on the upward
or downward movement of the spool (122), the fourth port (150)
transmitting the valve pressure (P3) to the corresponding hydraulic
motor (32), (42) as a control signal (34), (44).
2. The pendulum type wave-power generating apparatus according to
claim 1, wherein the hydraulic transmission comprises: a pump (20)
connected to a pendulum (11) that is swung in a pendulum motion by
variation of a wave; and the hydraulic motors (32) and (42)
respectively connected to the pipes (30) and (40) coupled to
opposite ends of the pump (20).
3. The pendulum type wave-power generating apparatus according to
claim 1, wherein the pressure accumulators (31) and (41)
respectively accumulate and store pressures (P1) and (P2) in the
pipes (30) and (40) of the hydraulic circuit.
4. The pendulum type wave-power generating apparatus according to
claim 1, wherein the pressure control valves (33) and (43) are
configured such that when the mean hydraulic pressures of the pipes
(30) and (40) connected to the hydraulic motors (32) and (42) of
the hydraulic transmission differ from each other and a difference
between the mean hydraulic pressures exceeds a preset limiting
value, a switching valve (50) communicates the pipes (30) and (40)
connected to the hydraulic motors (32) and (42) with each other so
that the mean hydraulic pressures in the pipes (30) and (40) of the
hydraulic motors (32) and (42) are equal to each other.
Description
TECHNICAL FIELD
The present invention relates, in general, to controllers for
pendulum type wave-power generating apparatuses. Wave-power
generation is a fascinating field that uses sea waves having high
energy density, but commercialization has been delayed by the
difficulty of reducing the cost of power generation. Wave power is
irregular wave energy, so it is difficult to handle it.
Commercialization is much more difficult, compared to other fields,
because of the severe environmental conditions of the sea. The
biggest problem is low power generation efficiency. Solving this
problem has been pointed out as the basic priority. The present
invention relates, more particularly, to a controller for pendulum
type wave-power generating apparatuses which controls the operation
conditions of a pendulum type wave-power generating apparatus in
response to the characteristics of sea waves so that high power
generation efficiency can always be maintained regardless of
variations in the state of the sea waves, thus reducing the cost of
power generation.
BACKGROUND ART
Sea waves are composite waves that are a combination of different
kinds of regular waves, but they are not completely irregular and
have spectrum structures in which most energy is concentrated
around regular waves of a specific height and frequency. Using such
characteristics, sea waves are converted into regular waves of the
same period as that of the center of the spectrum. The response of
wave-power generation with respect to the regular waves of
specified wave height and frequency is checked using antenna
theory. A method of commercialization has been discovered that
makes reference to the above behavior of the response. There is a
close correspondence between wave-power generation and the antenna.
The antenna theory can be used as an effective tool when
researching wave-power generation.
The problem is that sea waves are not regular. The waveform of sea
waves is distorted with respect to that of a sine wave. The wave
height and wave length are also not constant. However, in terms of
statistics, the wave nature can be obviously read from the sea
waves. Further, if the mean value is paid attention to, there is
regularity between the wave height and the wave period. For this
reason, sea waves are regarded as semi-regular waves and as a kind
of wave motion which continuously varies within a regular pattern.
Therefore, with regard to wave-power generation, if parameters of a
generation apparatus are adjusted (optimized) in response to
variation of characteristics attributable to the irregularity of
the sea waves, that is, in response to a variation in conditions,
satisfactory power generation can be automatically maintained. For
this, development of a controller for wave-power generating
apparatuses that can reduce the cost of power generation is
required.
DISCLOSURE
Technical Problem
Accordingly, the present invention has been made keeping in mind
the above problems occurring in the prior art, and a first object
of the present invention is to control the output volume value (the
size of output volume) of a hydraulic motor in response to a
variation in irregular sea waves such that the generation load is
optimized, thus automatically maintaining satisfactory power
generation, thereby reducing the cost of power generation.
A second object of the present invention is to cope with variation
in the state of sea waves without using a separate wave height
meter, in an effort to realize a reduction in the cost of power
generation. The wave height meter is not only very expensive but
also requires high technology to process obtained data, thus making
common on-line use of it difficult. If data about irregular waves
could be obtained without using a wave height meter, the practical
effect of a wave-power generating apparatus would be markedly
enhanced.
The above and other objects, features and advantages of the present
invention will be more clearly understood from the following
detailed description taken in conjunction with the accompanying
drawings. Furthermore, the objects, features and advantages of the
present invention can be realized by means disclosed in the
accompanying claims or combination thereof.
Technical Solution
In order to accomplish the above objects, the present invention
provides a controller for a pendulum type wave-power generating
apparatus converting a pendulum motion of wave-power energy into a
rotary motion using a hydraulic transmission that has pressure
accumulators (31) and (41) on a hydraulic circuit thereof, thus
operating a generator (60), the controller including: pressure
control valves (33) and (43) controlling output volumes of
hydraulic motors (32) and (42) that operate the generator (60) such
that the output volumes are proportional to mean hydraulic
pressures in pipes (30) and (40) of the hydraulic circuit so that a
mean value of wave-power energy input into the hydraulic circuit is
equal to a mean value of a drive force of the generator (60),
whereby wave-power energy is able to be used regardless of a
variation in wave conditions on the sea.
Advantageous Effects
As described above, a pendulum type wave-power generation apparatus
is characterized in that it can be constructed at a comparatively
low cost and the efficiency thereof is superior. For instance, in
the case of a unit apparatus, estimated unit generation cost has
been reported as being .ltoreq.0.085 $/kWh, so it has already
reached a practicable level.
A controller for pendulum type wave-power generating apparatuses
according to the present invention can further reduce unit power
cost compared to the level of the conventional technique. Thus, the
present invention can reliably eliminate the obstacle (the problem
of the high cost of power generation) to commercializing the
wave-power generation. Therefore, the present invention makes it
possible to devise a detailed plan for using wave-power energy as
well as measures to cope with stormy conditions, thus promoting the
commercialization of wave-power generation.
Furthermore, the controller for pendulum type wave-power generating
apparatuses according to the present invention has a simple and
strong structure, thus ensuring the sufficient durability against
conditions of the sea.
Moreover, thanks to the above-mentioned effects, use of wave-power
energy for purposes of commercialization that has been at a
standstill becomes possible. This also has an effect on
environmental preservation.
DESCRIPTION OF DRAWINGS
FIG. 1 is a system circuit view showing the structure of a pendulum
type wave-power generating apparatus provided with a controller for
pendulum type wave-power generating apparatuses according to an
embodiment of the present invention to improve the power generation
efficiency.
FIG. 2 is of front sectional views of an embodiment of a pressure
control valve showing an initial stage of operation of a pendulum
in which internal valve pressure is increasing.
FIG. 3 is of front sectional views showing an embodiment of the
pressure control valve which transmits a control signal of an
increase of the output volume of a hydraulic pump as the valve
pressure (P3) is reduced, according to the present invention.
DESCRIPTION OF THE ELEMENTS IN THE DRAWINGS
10: channel 11: pendulum 12: support point 20: hydraulic pump 21:
bed tank 30, 40: pipe 31, 41: pressure accumulator 32, 42:
hydraulic motor 33, 43: pressure control valve 44, 54: control
signal 50: switching valve 60: generator 100: first port 101: iris
diaphragm 102: plunger 110: cylinder 111: damper 112: thin hole
113: elastic member 114: lower chamber 115: upper chamber 120:
chamber 121: first elastic member 122: spool 123: second elastic
member 124: passage 130: second port 140: third port 150: fourth
port 160: drain pipe 170: tank recovery pipe P1, P2: pressure
(hydraulic pressure) P3: valve pressure
BEST MODE
The invention now will be described more fully hereinafter with
reference to the accompanying drawings, in which various
embodiments are shown. This invention may, however, be embodied in
many different forms, and should not be construed as limited to the
embodiments set forth herein. Furthermore, relative terms, such as
"front", "back", up", "down", "upper", "lower", "left", "right",
"lateral", etc., may be used herein to simplify the description of
the invention and describe one element's relationship to other
elements as illustrated in the Figures. It will be understood that
relative terms are intended to encompass different orientations of
the device in addition to the orientation depicted in the Figures.
It will be understood that, although terms, such as "first",
"second", "third" and "fourth", may be used herein to describe
various elements, these terms are not intended to attach relative
importance to the elements.
The present invention has the following characteristics in order to
achieve the above-mentioned objects.
Hereinafter, a preferred embodiment of the present invention will
be described in detail with reference to the attached drawings. The
terms and words used in the specification and claims are not
necessarily limited to typical or dictionary meanings, but must be
understood to indicate concepts selected by the inventor as the
best method of illustrating the present invention, and must be
interpreted as having meanings and concepts adapted to the scope
and sprit of the present invention for the sake of understanding
the technology of the present invention.
Therefore, the construction of the embodiment illustrated in the
specification and the drawings must be regarded as only
illustrative examples, which are not intended to limit the present
invention. Furthermore, it must be understood that various
modifications, additions and substitutions are possible at the
point of time of application of the present invention.
In an embodiment of the present invention, a pendulum type
wave-power generating apparatus converts pendulum motion of
wave-power energy into rotary motion using a hydraulic transmission
that has pressure accumulators 31 and 41 on a hydraulic circuit
thereof, thus operating a generator 60. A controller for the
wave-power generating apparatus includes pressure control valves 33
and 43 which control the output volumes of the hydraulic motors 32
and 42 that operate the generator 60 such that they are
proportional to mean hydraulic pressures in pipes 30 and 40 of the
hydraulic circuit so that the mean value of wave-power energy input
into the hydraulic circuit is equal to the mean value of the drive
force of the generator 60, thus making it possible to use
wave-power energy regardless of variations in the state of the
waves on the sea.
Furthermore, the pressure control valves 33 and 43 use the force of
the wave-power energy as input signals and transmit pressures
corresponding to the input signals to the generator 60 as output
signals, wherein the mean hydraulic pressures of the hydraulic
circuit are used as the input signals.
The hydraulic transmission includes: a pump 20, which is connected
to a pendulum 11 that swings in a pendulum motion resulting from
variations of the wave; the hydraulic motors 32 and 42, which are
respectively connected to the pipes 30 and 40 coupled to the
opposite ends of the pump 20; and the generator 60, which is
operated by the hydraulic motors 32 and 42.
The pressure accumulators 31 and 41 respectively accumulate and
store pressures P1 and P2 in the pipes 30 and 40 of the hydraulic
circuit.
The pressure control valves 33 and 43 are configured such that if
the mean hydraulic pressures of the pipes 30 and 40 connected to
the hydraulic motors 32 and 42 of the hydraulic transmission differ
from each other and the difference between the mean hydraulic
pressures exceeds a preset limiting value, a switching valve 50
communicates the pipes 30 and 40 connected to the hydraulic motors
32 and 42 with each other so that the mean hydraulic pressures in
the pipes 30 and 40 of the hydraulic motors 32 and 42 become the
same.
Each of the pressure control valves 33 and 43 includes: a first
port 100 which is connected to the corresponding pipe 30, 40 of the
hydraulic circuit and into which the hydraulic pressure P1, P2 is
input; a cylinder 110 into which the hydraulic pressure P1, P2 is
applied from the first port 100; a damper 111 which is installed in
the cylinder 110 and is moved upwards or downwards by the hydraulic
pressure P1, P2 applied thereto from the first port 100; a third
elastic member 113 which is contracted by the hydraulic pressure
P1, P2 applied to the damper 111 from the first port 100; a chamber
120 in which a spool 122 is moved upwards or downwards by the
damper 111, thus increasing or reducing a valve pressure P3 in the
chamber 120; first and second elastic members 121 and 123 which are
respectively installed on and under the spool 122 and are expanded
or contracted depending on the movement of the spool 122; a second
port 130 through which the hydraulic pressure P1, P2 of the
hydraulic circuit is applied into the chamber 120; a third port 140
which relieves the valve pressure P3 from the chamber 120 to the
outside; and a fourth port 150 which communicates with the second
port 130 or the third port 140 depending on the upward or downward
movement of the spool 122 and transmits the valve pressure P3 to
the corresponding hydraulic motor 32, 42 as a control signal 34,
44.
Each pressure control valve 33, 43 transmits the valve pressure P3
in the chamber 120, which is increased or reduced by the hydraulic
pressure P1, P2 transmitted through the first port 100 or the
second port 130, to a servo 35, 45 of the hydraulic motor 32, 42
through the fourth port 150 as a control signal. If the valve
pressure P3 is increased, the control signal is transmitted such
that the output volume is reduced. If the valve pressure P3 is
reduced, the control signal is transmitted such that the output
volume is increased.
The case where the output volume of the hydraulic motor 32, 42 is
increased refers to the case where as the wave-power energy
increases, the pressure in the pipe 30, 40 increases so that the
damper 120 and spool 122 are moved upwards by the hydraulic
pressure P1, P2 from the fist port, thus increasing the valve
pressure P3.
Hereinafter, the controller of the pendulum type wave-power
generating apparatus according to a preferred embodiment of the
present invention will be described in detail with reference to
FIGS. 1 through 3.
The controller of the pendulum type wave-power generating apparatus
according to the present invention converts the pendulum motion
into constant high-speed rotation using the hydraulic transmission,
thus operating the generator 60. The pressure accumulators (spring
pressure accumulators) 31 and 41 are provided on the hydraulic
circuit. The controller smoothens the output of power generation
using the characteristics of the pressure accumulators and,
simultaneously, calculates an incident wave from the mean value of
the circuit pressure (the mean hydraulic pressure in the hydraulic
circuit pipe) and controls the output volume of the hydraulic
motors 32 and 42 such that they correspond to the incident
power.
Eventually, regardless of wave conditions of the sea, the impedance
matching state can be maintained. The control signals that are
produced by determination, using the circuit pressures (the
pressures P1 and P2 in the pipes 30 and 40 of the hydraulic
circuit), of the pressure control valves 33 and 43 that are of the
controller of the pendulum type wave-power generating apparatus
after the pressure control valves 33 and 43 have given preset
operations to the hydraulic motors 32 and 42. All the signals that
are used are analog.
The pendulum type wave-power generating apparatus using the
controller of the present invention is focused on the wave nature
of the sea and accelerates the pendulum 11 using periodic
wave-power, thus generating the pendulum motion that resonates with
the wave. The hydraulic transmission converts the pendulum motion
into rotary motion, thus operating the generator 60. The apparatus
is characterized in that if two conditions of the resonance and
impedance matching are satisfied, the power generation efficiency
is maximized (in the same manner as that of an antenna). In other
words, the same method as optimizing the antenna can be used in the
wave-power generation. If the wave of the sea is constant like an
electric wave, the method of the antenna can be directly used in
the wave-power generation and the optimization of the system is
possible. However, because the waves of the sea cannot be constant,
the present invention uses the following means.
Statistical data about the sea waves that has been collected by a
separate process are organized, and characteristics of power, wave
heights and periods are arranged in a database. Here, the
characteristics are the mean of data obtained after have been
continuously measured for a predetermined time period (e.g., 20
minutes) rather than being obtained in a single measurement. Thus,
if such data is prepared, the mean wave height or the mean period
can be obtained, so that the mean power corresponding to them can
be determined. The present invention indirectly measures the mean
wave height without using a separate wave height meter, determines
the mean power using the wave height, and controls the hydraulic
motors 32 and 42 depending on the mean wave height so that the
output volumes of the hydraulic motors 32 and 42 are optimized.
Thereby, the efficiency of wave-power generation can be markedly
enhanced.
In the case of the waves of the sea, even each wave is irregular,
that is, the wave height and the period thereof vary. Given this,
the present invention uses a transmission circuit that is
configured such that the resonance and impedance matching of each
wave can be approximated. To achieve the above purpose, with regard
to individual waves, every time waves of different energies are
input, hydraulic energy corresponding to the energy of each wave is
accumulated in the pressure accumulators 31 and 41. The hydraulic
pressures accumulated in the pressure accumulators 31 and 41 are
respectively supplied to the hydraulic motors 32 and 42. If the
energy of the sea waves increases, the discharge rate of the pump
20 (the flow rate supplied to the hydraulic motors 32 and 42) is
increased, so that the mean pressure of the hydraulic circuit that
is provided with the hydraulic motors 32 and 42 (that is, the
pressures P1 and P2 in the pipes 30 and 40 of the hydraulic
circuit) is increased. If the output volumes of the hydraulic
motors 32 and 42 are extended so that the outputs of the hydraulic
motors 32 and 42 are increased, the consumption flow rate
increases, thus reducing the mean pressure of the hydraulic circuit
(of the pipes 30 and 40 of the hydraulic circuit). The mean
pressure of each of the pipes 30 and 40 of the hydraulic motors
also is a parameter that indicates the status of supply and demand
of energy used in the generation. In the present invention, this
parameter is used as a control signal.
In the present invention, assuming the operation of a typical
three-phase induction generator, a simple hydraulic transmission
providing constant speed operation is used. Therefore, the output
(Lm) of the hydraulic motor at a constant speed is proportional to
the torque of the motor. The torque (TM) of the motor is
proportional to a multiple of the pressure (P) by the output volume
(Dm) of the motor, so that the output (Lm) of the hydraulic motor
at a constant speed is proportional to P.times.Dm. The present
invention realizes the desired control using this relationship.
Conditions of the Wave-Power Generating Apparatus According to the
Present Invention
In order to realize the production of the present invention on a
commercial scale, enhancing the reliability of the product must be
focused on. For this, in terms of an increase in the reliability
for the price, it is preferable that among standardized products of
high quality, appropriate parts be selected and used as parts of
the apparatus. The hydraulic motors 32 and 42 used in the present
invention refer to standardized products that comply with the above
policy. Each hydraulic motor 32, 42 has a characteristic that adds
or subtracts the output volume (Dm) of the motor using a pressure
signal (analog). Hence, the control method of the present invention
is to control the output volume (Dm) of each hydraulic motor 32, 42
using the pressure signal (analog) of the pressure control valve
33, 43. The desired control can be easily implemented by the
hydraulic analog method, but also the control signal 34, 44 is
transmitted through the thin pipe (connected to the fourth port 150
of the pressure control valve), so that there is no problem even
though it is exposed to the sea water. Based upon the premise that
the above-mentioned hydraulic motor has high reliability and a
simple structure, the present invention will be commercially
available as a standardized product.
As characteristics of the sea waves, variation of the wave height
and variation of the wave period are related to each other. If the
observational station is fixed, the larger the wave height, the
longer the wave period. In the wave-power generating apparatus, the
energy of the incident wave is designated by a mathematical
function in two kinds of variables of the wave height and the wave
period. Therefore, the method of measuring the two kinds of
variables and conducting the generation control using these values
must be precise. The controller of the present invention
intentionally uses only the value of the wave height in
consideration of the performance against the costs. The reasons for
this is as follows.
As stated above, the power (from 10 to 20 times the design rating
power) of the sea waves, for example, in a storm, may destroy the
apparatus. Thus, a positive incident power-cut is needed to enhance
the safety. If the power of the sea waves exceeds the design rating
power, it is required to reduce the input power rather than to
increase the power generation efficiency. As such, requiring the
control effect of the present invention is limited to normal
conditions in which the power of the sea waves is within the design
rating power. Hence, a normal `control error` attributable to not
using data about the period of the waves can be disregarded in
practical use.
If data about the period of the waves is not used, although some of
the characteristics may be sacrificed, there is an advantage
sufficient to overcome the sacrifice in that the apparatus can be
simplified.
The power (force of the wave-power energy)(per unit width) of the
sea waves: W (kW/m) is expressed by the following Equation (1).
W.apprxeq.0.5H.sub.1/3.sup.2T.sub.1/3 Equation (1)
(where H.sub.1/3: significant wave height (m), T.sub.1/3:
significant wave period (s))
The controller of the pendulum type wave-power generating apparatus
according to the present invention conforms the case where
T.sub.1/3: significant wave period=a constant in Equation (1).
Therefore, W is regarded as being proportional to H.sub.1/3.sup.2.
The sea waves having such characteristics act as the input, thus
operating the pendulum 11. Then, the pendulum 11 swings and absorbs
wave-power energy. The absorbed power: E (kW) is expressed as the
following Equation (2).
E=2.times.10.sup.-3T.sub.p.theta..sub.0/T.sub.1/3 Equation (2)
(where T.sub.p: the mean value (Nm) of load torque applied to the
pendulum shaft, .theta..sub.0: a swing angle (radian) of the
pendulum)
If the load applied to the pendulum is controlled so that Equation
(1)=Equation (2), in other words, if W=E Equation (3) is satisfied,
the efficiency of wave-power generation can be maximized (impedance
match). Because the pendulum 11 operates the pump 20 of the
hydraulic transmission, the mean value T.sub.p of load torque
applied to the pendulum shaft is proportional to the mean value of
the output pressure of the pump 20. In this case, a proportional
constant is appropriately selected such that the swing angle
.theta..sub.0 of the pendulum is proportional to the wave height
H.sub.1/3 and Equation 3 is satisfied (the value of the
proportional constant is determined by characteristics of the
pressure accumulators 31 and 41). The swing angle, the load torque
and the hydraulic pressure of the pump 20 are proportional to the
wave height, and the input of the pump 20 is proportional to the
square of the wave height. As shown in Equation (1), in response to
a variation in the wave height of the incident wave, the incident
power varies in proportion to the square of the wave height, but
because the swing angle of the pendulum 11 and absorption power are
proportional to the square of the swing angle, the swing angle is
proportional to the wave height. Further, if the proportional
constant is appropriately determined, the incident power becomes
equal to the absorption power. In other words, impedance matching
is satisfied.
If the discharge rate of the pump 20 and the mean values of the
consumption rates of the hydraulic motors 32 and 42 are balanced,
the mean values of the pressures P1 and P2 in the hydraulic circuit
pipes 30 and 40 become constant. An excess or deficiency amount is
regulated by absorption or discharge of the pressure accumulators
31 and 41 and expressed as a variation in pressure. In this case,
Equation 3 must also be satisfied to realize the high efficiency
operation. Here, if the consumption rates are increased or reduced
by adjusting the output volumes of the hydraulic motors 32 and 42
in response to the variation of the mean values of the pressures P1
and P2 of the pipes 30 and 40 so that the state of Equation (3) is
satisfied, the high efficiency operation can be automatically
maintained. That is, if the wave height is varied by variations in
the conditions of the sea, the mean values of the pressures P1 and
P2 of the pipes lose the balance and will vary. At this time, the
pressure control valves 33 and 43 of the present invention
increases or reduces the output volume (the size of output volume)
of the hydraulic motors 32 and 42 in response to the pressures P1
and P2 of the pipes of the hydraulic circuit, thus reviving the
impedance matching conditions, thereby stabilizing the mean value
of each pipe pressure P1, P2 at another predetermined value.
FIG. 1 is a system circuit view showing the structure of the
pendulum type wave-power generating apparatus provided with the
controller according to the embodiment of the present invention to
improve the power generation efficiency. This will be explained in
detail below.
The apparatus converts wave-power energy into the swing energy of
the pendulum 11 and converts it into continuous rotary motion using
the hydraulic transmission, thus operating the generator 60,
wherein because of the two factors of: {circle around (1)} the
wave-power energy being efficiently used for the operation of the
generator 60; and {circle around (2)} preventing period variation
from occurring in the generation output are satisfied, the
apparatus can be of practical use. The structure and operation of
the power generation system having the controller of the pendulum
type wave-power generating apparatus according to the present
invention will be described with reference to FIG. 1.
Referring to FIG. 1, waves enter the apparatus from the right side
of a channel 10 and apply wave-power to a flat board of the
pendulum 11 which pivots around a support point 12 at the left side
of the channel 10, thus swinging the pendulum 11. This pendulum
motion is transmitted to the pump (hydraulic pump 20). The pump 20
sucks oil from a bed tank 21 and alternately sends pressing oil to
the pipe (30, referred to as `the first pipe` for the sake of
explanation, Pressure P1) or the pipe (40, referred to as `the
second pipe` for the sake of explanation, Pressure P2) depending on
the direction in which the pendulum 11 moves. The pressure
accumulator 31 is provided on the first pipe 30. The hydraulic
motor 32 is connected to the first pipe 30. The pressure
accumulator 41 is provided on the second pipe 40. The hydraulic
motor 42 is connected to the second pipe 40. The hydraulic motors
32 and 42 operate as a pair on the generator 60. Because there is a
phase difference of 180.degree. between the hydraulic motors 32 and
42, periodic torque variations of the hydraulic motors 32 and 42
are offset by overlap between the two motors. Thereby, the output
of power generation can become smooth. One stroke of the oil
discharge of the pump 20, for example, includes discharging oil for
a 1/2 T second to the hydraulic motor 32, and resting for a
subsequent 1/2 T second (the discharge rate per one stroke
corresponds to the amount required to continuously rotate the
hydraulic motor 32 for the one period of a T second). Because the
flow rate of the hydraulic motor 32 is constant and the
instantaneous discharge rate of the hydraulic pump 20 varies, a
difference in the flow rate therebetween is accumulated in the
pressure accumulator 31. Of course, the case of the hydraulic motor
42 is the same as that of the hydraulic motor 32.
The pressure accumulator 31 connected to the first pipe 30 and the
pressure accumulator 41 connected to the second pipe 40 are of the
spring type, wherein each increases the pressure in proportion to
the volume of oil accumulated therein, and accumulated energy is
proportional to the square of the volume of oil accumulated
therein. Thus, the pressure of the first pipe 30 varies depending
on the size of the volume of oil accumulated in the pressure
accumulator 31. The pressure of the second pipe 40 varies depending
on the size of the volume of oil accumulated in the pressure
accumulator 41.
If the incident wave height is increased by variation in the
conditions of the sea, the swing angle of the pendulum 11 and the
discharge rate of the hydraulic pump 20 are increased. Because the
required flow rates of the hydraulic motors 32 and 42 are constant,
extra oil accumulates in the pressure accumulators 31 and 41, so
that the mean value of the pressure p1 in the first pipe 30 and the
mean value of the pressure P2 in the second pipe 40 are increased.
The pressure control valve 33 receives the pressure P1 as a control
signal and controls the output volume Dm of the hydraulic motor 32
using its output signal, thus increasing the required flow rate of
the hydraulic motor 32. As a result, the discharge rate of the
hydraulic pump 20 is balanced with the required flow rate of the
hydraulic motor 32, so that the mean value of the pressure P1 of
the first pipe 30 is stabilized at a new value.
In the same manner, the pressure control valve 43 receives the
pressure P2 in the second pipe 40 as a control signal and controls
the output volume Dm of the hydraulic motor 42, thus increasing the
required flow rate of the hydraulic motor 42. As a result, the
discharge rate of the hydraulic pump 20 is balanced with the
required flow rate of the hydraulic motor 42, so that the mean
value of the pressure P2 of the second pipe 40 is stabilized into
another new value.
Energy Ew (kNm) of an incident wave applied to the pendulum 11 of a
width B for a period of a T second is expressed by the following
Equation (4).
E.sub.W.apprxeq.0.5.times.H.sup.2.times.T.sup.2.times.B (kNm)
Equation (4)
(where H: a significant wave height (m), T: a significant wave
period (s), B: width (m) of the pendulum)
If it is assumed that oil (volume V) discharged from the pump 20
has accumulated in the pressure accumulators 31, 41 once, energy
E.sub.0 of the discharge oil is expressed as the following Equation
(5). E.sub.0=(Ap).sup.2/(2k)=kV.sup.2/2A.sup.2 (Nm) Equation
(5)
(where A: an area (m.sup.2) of a piston of the pressure
accumulator, P: hydraulic pressure (Pa), k: spring constant
(N/m))
The hydraulic pressure P is proportional to a displacement x of the
piston in the pressure accumulator 31, 41 (therefore, it is
proportional to the volume V of oil accumulated in the pressure
accumulators 31, 41).
In the above-mentioned system structure, when the spring constant
of the spring of the pressure accumulator is adjusted such that the
mean value of the pressure P1 or the mean value of the pressure P2
when in the normal conditions is proportional to the incident wave
height, and when Equation (3) is satisfied, the conditions becomes
as follows.
(1) The size of the swing angle of the pendulum is proportional to
the incident wave height.
(2) The power of the incident wave is proportional to the square of
the incident wave height.
(3) The power absorbed by the pendulum is proportional to the
square of the pressure of the pressure accumulator.
(4) The efficiency of the wave-power generation becomes
maximized.
In other words, as is well known, when the mean value of the
pressure P1 or the mean value of the pressure P2 is proportional to
the wave height, the swing angle of the pendulum is also
proportional to the wave height. E.sub.W of Equation (4) is
proportional to the square of the wave height H, E.sub.0 of
Equation (5) is proportional to the square of the volume V, and the
volume V is proportional to the weight height H. Therefore, if an
appropriate parameter is selected, in the state in which the
parameter is fixed, the conditions of the impedance match, such as
Equation (6) that is derived from Equations (4) and (5), are
satisfied within a wide range of wave heights H. E.sub.W=E.sub.0
Equation (6)
In this state, to promote the stable power generation, the output
volume Dm of each hydraulic motor 32, 42 is increased or reduced
depending on the variation in the discharge rate of the pump 20.
The purpose of the pressure control valves 33 and 43 is to achieve
the above purpose. The pressure control valve 33 increases or
reduces the output volume of the hydraulic motor 32 using the servo
35, and the other pressure control valve 43 increases or reduces
the output volume of the hydraulic motor 42 using the servo 45.
The pressure P1 in the first pipe is determined by the volume of
oil accumulated in the pressure accumulator 31, and the pressure P2
in the second pipe is determined in the same manner as that of the
pressure P1. However, after the apparatus has been operated for a
long period of time, the pressures in the first and second pipes
may vary. The reason for this is because although there is slight
oil leakage, errors accumulate over a long period of time. If this
compounding is neglected, power distribution between the two
hydraulic motors 32 and 42 becomes unbalanced. To prevent this
problem, the switching valve 50 compares the control signal 34 of
the pressure control valve 33 and the control signal 44 of the
pressure control valve 43, and if the difference between the two
exceeds a predetermined limit, the switching valve 50 connects the
first pipe to the second pipe, thus equalizing the pressures in the
two pipes. After the pressures in the two pipes have been
equalized, the connection between the two pipes is interrupted.
Thereby, the balanced load distribution to the two hydraulic motors
32 and 42 can be automatically maintained.
FIGS. 2 and 3 are front sectional views showing the pressure
control valve according to the present invention. In detail,
although FIG. 2 illustrates one of the pressure control valves that
is provided on the first pipe 30, the principle and structure
thereof are the same as those of the pressure control valve
provided on the second pipe 40. The pressure control valve includes
a part which extracts the mean value of the pressure (hydraulic
pressure, P1) (which is periodically varying) in the first pipe
using a displacement of plunger 102, and a spool type pressure
control valve which converts the displacement into hydraulic
pressure.
Of the pressure control valves, FIG. 2 will be explained with
reference to the pressure control valve 33 provided on the first
pipe 30. As shown in FIG. 2, the plunger 102 is placed upright in
the lower end of the pressure control valve 33, and the hydraulic
pressure P1 of the first pipe 30 that has passed through an iris
diaphragm 101 pushes the plunger 102 upwards with a force
proportional to the pressure P1. This force is transmitted to the
third elastic member 113 via the damper 111 and makes an upward
displacement proportional to the pressure (hydraulic pressure, p1).
This is the pressure accumulator provided with a small damper. This
displacement is transmitted to the second elastic member 123 which
biases the spool 122 upwards, thus increasing or reducing the force
of the second elastic member 123. The spool 122 may communicate the
fourth port 150 of the pressure control valve 33 with the second
port 130 or communicate the fourth port 150 with the third port
140. This operation is governed by the combination of three kinds
of axial forces including the first and second elastic members 121
and 123 that are applied to the spool 122 and the valve pressure P3
in the chamber 120.
At the initial stage of the operation of the pendulum 11, as shown
in FIG. 2, because the first elastic member 121, which generates a
constant and strong axial force, biases the spool 122 downwards,
the second port 130 communicates with the fourth port 150, so that
the pressure P1 is high when applied to the second port 130 through
the first pipe 30 and applied towards P3 of the chamber 120.
Thereby, the valve pressure P3 in the chamber 120 is increased,
thus pushing the spool 122 upwards in the chamber 120. Thus, the
second port 130 that has been connected to the first pipe 30 is
closed, so that the increase in the valve pressure P3 in the
chamber 120 stops. At this time, the magnitude of the valve
pressure P3 is proportional to the intensity of the resultant force
applied to the spool 122 downwards.
On the other hand, the valve pressure P3 may decrease. As shown in
FIG. 3, in an embodiment, when the pressure in the first pipe 30
increases and the pressure p1 is applied into the first port 100,
thus moving the plunger 102 upwards, the damper 111 is moved
upwards. Then, the third elastic member 113 is compressed and a
damper guide 116 is moved upwards, so that the second elastic
member 123 is compressed and the force of the second elastic member
123 offsets the force of the first elastic member 121 that biases
the spool 122 downwards, thus reducing the valve pressure P3 in the
chamber. At this time, the valve pressure P3 is used as the control
signal 34 of the output volume of the hydraulic motor 32 and is
transmitted through the fourth port 150. In this case, as the
wave-power energy increases, the discharge rate of the hydraulic
pump 20 is also increased. Thus, the reduced valve pressure P3 in
the pressure control valve 33 is transmitted as the control signal
through the fourth port 150 connected to the servo 35 of the
hydraulic motor 32. Thereby, the output volume of the hydraulic
motor 32 is increased. Of course, in the case where the valve
pressure increases, the reduced valve pressure P3 in the pressure
control valve 33 is transmitted as the control signal 34, so that
the output volume of the hydraulic motor 32 is increased (of
course, as shown in FIG. 1, the first pipe 30 that transmits the
pressure P1 to the pressure control valve 33 and the second pipe 40
that transmits the pressure P2 to the other pressure control valve
43 are connected to the switching valve 50, so that when signals
are transmitted from the pressure control valves 33 and 43, the
pressures (hydraulic pressures P1 and P2) in the first and second
pipes 30 and 40 are applied to the switching valve 50, and a member
in the switching valve 50 is thus moved in one direction, thus
connecting the first and second pipes 30 and 40 to each other,
thereby balancing the pressures P1 and P2 in the first and second
pipes 30 and 40 that have become unbalanced).
In other words, this embodiment illustrates the case where when the
valve pressure P3 is high, the output volume Dm is small, and as
the valve pressure P3 is reduced, the output volume Dm is increased
(of course, as stated above, the principle of the above-mentioned
operation is also applied in the same manner to the pressure
control valve 43 provided on the second pipe 40).
Although the hydraulic pressure (pressure P3) of the first pipe 30
periodically varies at wave period T, the present invention is
configured such that the variable constituent is prevented from
being transmitted to the valve pressure P3. To achieve the above
purpose, the present invention is provided with the damper 111. The
damper guide 116 is provided on the upper end of the damper 111.
The damper 111 uses the inner surface of the cylinder 110 as a
guide surface and is guided by the damper guide 116, so that the
damper 111 can be smoothly moved upwards or downwards by the
movement of the plunger 102.
The interior of the cylinder 110 is partitioned into a lower
chamber 114 and an upper chamber 115 by the damper 111. A strong
damping operation is conducted by oil flowing along a thin hole 112
which is formed between the two chambers. Thereby, the periodic
variable constituent of the sea wave is eliminated, and the valve
pressure P3 corresponding to the mean values of the conditions of
the sea waves per unit time (for example, the mean values when
waves are input five to ten times) can be simply obtained.
The Embodiment of the Present Invention and Specifications of this
Case
In the case of the incident wave height H=2 m, the incident wave
period T=6 s, the coast of the water depth h=3 m and the pendulum
width B=4 m, the power Pw of a wave applied to the pendulum
11.apprxeq.96 kW. This value is a short-time means value and takes
into account the characteristics of the sea waves. It is greater
than a long-time mean value obtained from Equation (4). The
amplitude .theta..sub.0 of the pendulum 11.apprxeq.40.degree. to
60.degree.. The power of the generator 60 is 40 kW (three-phase
induction AC generator, six pole, 1200 rpm (maximum)), as it is
expected that the efficiency .eta. of the generator 60=power
generating output/incident wave input.apprxeq.42%. A6VM55 (Dm=54.8
cm.sup.3/rev, maximum) of Rexroth company of Germany is used as
each hydraulic motor 32, 42. The capacity of each pressure
accumulator 31, 41 is 10 liters, and the maximum pressure thereof
is 20 Mpa. In each pressure control valve 33, 43, the diameter of
the spool 122 ranges from 10 mm to 20 mm. This is not large as a
control element.
Although the preferred embodiment of the present invention has been
disclosed for illustrative purposes, those skilled in the art will
appreciate that various modifications, additions and substitutions
are possible, without departing from the scope and spirit of the
invention as disclosed in the accompanying claims.
* * * * *